This makes sure that debug info and interpreter handle are created
lazily, even when interpretation is triggered by a different Isolate
sharing the same WasmEngine (and hence the native module).

R=titzer@chromium.org
TEST=mjsunit/wasm/worker-interpreter
BUG=v8:7424

Change-Id: Iba17e207a537007fd2e642cede22dad7a708c6c7
Reviewed-on: https://chromium-review.googlesource.com/1181045
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55220}